1. Field of the Invention
The present disclosure relates to an image forming apparatus that uses an electrophotographic recording method such as laser printer, a copier, or a facsimile, and particularly relates to image carrier cleaning.
2. Description of the Related Art
Examples of image forming apparatuses include apparatuses in which a toner image of different colors is formed on a photosensitive member, is primarily transferred to an intermediate transfer member that is an image carrier, and is subsequently secondarily transferred to a recording material. Examples of these kinds of image forming apparatus include apparatuses in which a cleaning unit is provided in order to remove remaining toner that remains on the intermediate transfer member without being transferred from the intermediate transfer unit to the recording material. A cleaning blade that is part of the cleaning unit is made of a rubber such as polyurethane, and due to the toner penetrating the edge of the blade, a lubricating effect can be demonstrated and preferable cleaning performance can be obtained.
However, if a state in which there is a small amount of toner penetrating into the edge of the cleaning blade continues, friction between the cleaning blade and the intermediate transfer member increases and a stick-slip phenomenon occurs. The stick-slip phenomenon occurs when the intermediate transfer member moves while the cleaning blade is pressed against the intermediate transfer member. Specifically, due to the friction between the cleaning blade and the intermediate transfer member, the edge of the cleaning blade deforms in the direction of movement of the intermediate transfer member (shear deformation, compression deformation). Energy that has accumulated at the edge due to this deformation functions as a restoring force (rebound elastic force), and the cleaning blade is returned to its original state. The stick-slip phenomenon is the phenomenon of repeating the deformation and the return to the original state. If this phenomenon progresses, the edge of the cleaning blade will jump, toner will slip through, and a cleaning defect will occur. Furthermore, sometimes the edge of the cleaning blade and the surface of the intermediate transfer member will be damaged. Furthermore, it is possible for the edge of the cleaning blade to be caught on the intermediate transfer member, causing the cleaning blade to curl up.
For this reason, Japanese Patent Laid-Open No. 2011-064741 discloses a configuration for preventing the occurrence of cleaning defects by supplying toner that functions as a lubricant to the cleaning blade. If toner is supplied to the cleaning blade, the toner image that has been formed on the intermediate transfer member comes into contact with a secondary transfer roller for transferring the toner image to a recording material, and accordingly, the toner is attached to the secondary transfer roller. When a recording material that is to be printed on next passes between the intermediate transfer member and the secondary transfer roller, the toner attached to the secondary transfer roller is transferred to the underside of the image forming surface of the recording material, or so to speak, smearing of the underside occurs.
Japanese Patent Laid-Open No. 2011-064741 discloses a configuration in which the secondary transfer roller is separated from the intermediate transfer member, and a configuration in which a bias is applied which has a polarity opposite to that at the time of transfer from the secondary transfer roller when a toner image comes into contact with the secondary transfer roller, in order to prevent or suppress the attachment of toner to the secondary transfer roller.
However, configurations in which the secondary transfer roller is separated from the intermediate transfer member are costly. Also, if image formation is performed repeatedly, throughput is affected due to the secondary transfer roller coming into and out of contact with the intermediate transfer member. Furthermore, an image defect can occur due to a shock at the time of contact. Additionally, even if a bias having a polarity opposite to that during the transfer from the secondary transfer roller is applied, there is a possibility that the attachment of toner to the recording material cannot be sufficiently suppressed and smearing of the underside will occur, depending on the amount of toner.